This invention relates in general to centrifugal clutches, and in particular to an automatically acting two way centrifugal clutch for transferring torque between the output of a motor and a rotating member.
Clutches have long been used to selectively transfer rotary drive power from the motor of a vehicle to its driving wheels. In particular, lightweight and inexpensive engines have been used for many years for driving small motorized vehicles such as bicycles, wheelbarrows, and motorcarts; and these engine-powered vehicles have in the past been equipped with clutches which automatically (a) crank the engine when the vehicle is initially moved in a working direction, (b) provide an idle condition or state in which the engine is mechanically disconnected from the drive wheels whenever it operates at a speed in a predetermined idle speed range, and (c) transfer torque from the engine to the vehicle driving wheels when the engine speed is increased beyond a predetermined or preselected maximum idle speed (the run or drive condition).
In general, the early automatic clutches use a pair of rotating clutch assemblies, each assembly having a friction surface for engaging a clutch drum in both the starting and driving modes of operation. A few of the early automatic clutches have two friction surfaces, one for the starting mode and one for the driving mode of operation. Each of the surfaces is generally associated with a separate pivoted clutch element, a pair of elements comprising a clutch assembly. In these clutches, as described in British Pat. No. 894,071, published Apr. 18, 1962, one of the friction surfaces is driven by the clutch drum to start the engine and the second surface is driven by the drive motor once the motor attains sufficient rotational speed, to transfer torque to the vehicle wheels when the speed of the engine is increased beyond a selected speed.
As a further variation in the construction of automatic centrifugal clutches, the apparatus described in French Pat. No. 1,169,492, published on Dec. 29, 1958, reflects the need for a clutch at a time when maintaining a stable idle speed range over the life of the bicycle was not a major concern. This clutch uses integral clutch members, each having two friction surfaces and connected by springs configured to provide a differential spring system having an idle speed range very sensitive to manufacturing tolerances. However, at that time, about 1958, the idle condition or state was apparently not used very much and hence the limited idle range caused no significant problems.
The apparatus disclosed in the French patent does not lend itself, however, to today's modern engine speeds or today's traffic patterns which can require long idle periods, for example, at red traffic lights. Thus, today, the clutch/spring configuration of the French apparatus, wherein the springs are located close to the clutch drum and outside the clutch member pivot points, have relatively large spring constants, and have small spring elongation relative to clutch member movement, is unacceptably sensitive to manufacturing tolerances and other alignment errors. The French design would likely, after long idle periods, tend to wear and produce heat at the drum surface, and the engine speed would have to be raised to bring the clutch surface into a definite drive position with the clutch drum.
It is therefore a principal object of this invention to provide an automatic clutch apparatus designed to have a definite and well defined idle condition or zone. Other objects of the invention are to provide an automatic two way acting centrifugal clutch which is reliable, which has a long lifetime, which will not wear out during long idle periods, which is low in manufacturing cost, and which can be used with lightweight vehicles.